It is well known that an increasingly important consideration in the production and use of integrated circuits (ICs) is the package in which the IC resides. The module or casing in which the IC is packaged is an important factor in the ultimate cost, performance and lifetime of the IC. A significant concern as the circuits become denser is that the number of leads to the package and connections from the leads to the integrated circuit pads increases; thus increasing the complexity of construction and adding to the cost of the end product, not just in terms of increased and more expensive materials, but also increased production costs.
The use of conventional, relatively heavy or robust lead frames for integrated circuits or other devices having high input/output (I/O) count is a problem because the inner portions of the leads are limited by their thickness in how closely they may be spaced. It has been proposed to narrow the interior portions of these leads, but this requires special machining or etching of the leads or special tooling.
Tape automated bonding (TAB) has also been extensively studied as a technique for providing very fine connections to the bonding pads of an IC chip. However, TAB tape has the disadvantage at the opposite end of the lead, namely the distal or external leads extending from the package are very fragile and easily damaged and difficult to mount to the printed circuit board (PCB) mounting pads. Additionally, to make the TAB connection directly to the IC bonding pads, the bonding pads, the inner ends of the delicate TAB leads or both must be provided with bonding bumps of gold, copper, tin, or mixtures thereof, or the like, to make an adequate connection. Providing bumps on the chip or the leads has always proved difficult because of their fine pitch for the chips with high numbers of bonding pads (I/O count).
Even the use of conventional wire bonds has proven less than desirable as the connection count has risen. As the number of required connections has grown, the distance from the bonding pads to the inner lead tips has increased, in turn increasing the wire bond lengths. Long wire bond lengths are not preferred because susceptibility to damage during assembly and wire sweep during the mold operation. During encapsulation or molding, the mold compound sweeps over the wires tends to push them. If they are long enough, they may contact each other or the IC chip and cause shorting, which affects circuit performance.
Thus, a continuing goal in the art of providing packages for electronic components such as integrated circuits is a package design that will address these multiple goals satisfactorily in an arrangement that can be reliably manufactured at the lowest cost. The lowest cost packages are those which have plastic bodies which can be molded from thermoplastic and thermoset materials.